Charges after 4 days

I can't believe that on an unlimited minutes, texts and 4gb of data that I could have been charged 80p in 4 days. It's a bit worrying as scaled up this is likey to cost around £6 extra a month. Am I being subjected to some sneaky charges I don't know about? I know it's not mms (not sent pictures), it's not premium rate numbers or any text service so why could it be? Good job I'm still in the cooling off period as if it doesn't stop I could be voting with my feet.